The present invention relates to heat exchangers for use in automobile air conditioning circuits and to configurations for improving refrigerant distribution through the heat exchanger.
Automotive heat exchangers or evaporators include a plurality of refrigerant tubes connected typically to two headers or tanks. One header has an inlet for receiving refrigerant while the other header has an outlet for evacuating refrigerant from the evaporator. Heat dissipation fins are disposed between the refrigerant tubes to facilitate heat exchange between the evaporator and the ambient air.
In operation, refrigerant flows into the inlet through the refrigerant tubes where heat contained within the ambient air is exchanged with the refrigerant, thereafter the refrigerant leaves the evaporator through the outlet. Inertial and gravitational forces in the headers of the evaporator separate the liquid from the vapor phase of the refrigerant causing a mal-distribution of the liquid phase throughout the heat exchanger tubes. Consequently, a number of the refrigerant tubes will dry out prematurely and then superheat. The superheated refrigerant reduces heat transfer from the ambient air to the refrigerant. Furthermore, the refrigerant tubes containing single phase vapor have a heat transfer coefficient that can be three times lower than the corresponding two-phase (i.e. liquid/vapor) flow conditions. Uniform two-phase flow distribution can improve heat transfer rates up to thirty percent as compared to a completely separated single phase flow and in turn improve performance of the evaporator reducing the overall power consumption of the compressor. The improved efficiency of the refrigerant system not only reduces energy consumption but can lead to a reduced evaporator size while still providing the same performance both in terms of capacity and coefficient of performance. A smaller evaporator is advantageous as space is a premium within the vehicle and specifically underneath the instrument panel.
In order to address the mal-distribution problem described above, prior art evaporators have utilized a four pass refrigerant flow configuration. While the four pass configuration minimizes the mal-distribution of the refrigerant in the evaporator, this four pass configuration increases the pressure drop across the evaporator core due to the increased velocity of the refrigerant and superheated refrigerant expanding towards the latter part of the evaporator. Furthermore, one half of the core is in parallel flow and the other half is in counter-flow with respect to the ambient air flow direction through the heat exchanger. A counter-flow circuit has a better heat transfer rate than a parallel flow circuit.
Therefore, what is needed is a new and improved evaporator design which corrects the mal-distribution problem described above while providing a low pressure drop across the evaporator core and a counter-flow circuitry.
In an aspect of the present invention, an evaporator for exchanging heat between a refrigerant and ambient air is provided. The evaporator includes a plurality of refrigerant tubes at least two header tanks in fluid communication with the plurality of refrigerant tubes.
In another aspect of the present invention at least one of the heater tanks has a plurality of perforations through which refrigerant flows into each of the plurality of refrigerant tubes and a plurality of fins dispersed between each of the plurality of refrigerant tubes.
In yet another aspect of the present invention each of the plurality of refrigerant tubes are formed in a U-shape and includes at least one of the header tanks having an inlet for receiving refrigerant into the evaporator and at least one of the header tanks having an outlet for expelling refrigerant from the evaporator.
In yet another aspect of the present invention the perforations in the distribution tube has slots/perforations and the slots/perforations in the distribution tube that is disposed in the header tank have varying depth.
In still another aspect of the present invention the slot in a center of the header tank has the largest depth and the depth of the slots progressively decreases moving from the center toward the end of the header tank.
In yet another aspect of the present invention the slot/perforation has depth arrangement in accordance with that shown in FIG. 6.
In yet another aspect of the present invention the distribution tube can be rotated between xe2x88x9235 degrees and +35 degrees from a vertical position without degrading the evaporator""s performance.
In yet another aspect of the present invention a plurality of internal turbulators are formed from a piercing operation. The turbulators turbulate (produce turbulent flow) the two phase flow and directs the flow through the slots/perforations located in the beginning and middle of the distribution tube. Without these turbulators, two phase refrigerant will flow to the bottom of the tube first and then to the rest of the perforations causing mal-distribution.
These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings.